The invention relates to fluid filters, and more particularly to constructions maximizing flow capacity and minimizing restriction.
There is continuing demand for increased flow capacity in the same or even smaller size filters. This is particularly true in air cleaner designs for internal combustion engines, where engine compartment space is limited. A filter construction enabling higher capacity in the same or less space provides competitive advantage and a space efficient filter system.
A common air cleaner used in truck engines has a filter element provided by pleated filter media having a plurality of pleats in a closed loop configuration, typically annular, having an outer perimeter defined by a plurality of outer pleat tips, an inner perimeter defined by a plurality of inner pleat tips, and a hollow interior extending along an axis. The air typically flows laterally or radially inwardly through the filter media into the hollow interior and then axially outwardly through an outlet flow tube to the combustion air intake of the engine. The outlet tube has a diameter slightly smaller than the diameter of the hollow interior between the inner pleat tips. A first end cap covers the axial ends of the pleats at one axial end of the filter element and forms a radial seal with the outlet tube extending therethrough partially into the hollow interior. Additionally or alternatively, the end cap forms an axial seal with the housing containing the filter element. The end cap is a resilient compressible material, to aid in forming the noted seals. The radial seal is formed by radially compressing the end cap material between the outlet tube and the inner pleat tips or an inner liner extending therealong. The axial seal is formed by axially compressing the end cap material between the axial ends of the pleats and the axial end of the housing containing the filter element. A second end cap covers the axial ends of the pleats at the other axial end of the filter element and may span the hollow interior to close same, or such hollow interior may be closed by a portion of the housing extending thereinto. The flow capacity of the filter is affected by various factors, including restrictions, such as the size of the outlet opening through the earlier noted outlet tube at the axial end of the filter.
The invention of commonly owned copending U.S. application Ser. No. 09/240,714, filed Jan. 29, 1999, now U.S. Pat. 6,149,700, increases flow capacity by enabling enlargement of the outlet flow passage, to lower the noted restriction to flow. The increased outlet size of the filter element and lowered restriction is accomplished while still maintaining or even increasing the amount of filter media and while also staying within the same package or housing size. As noted above, in the prior art, the largest diameter outlet from the filter element is limited to approximately the size of the diameter of the hollow interior defined by the inner pleat tips. In the preferred embodiment of the invention of the ""714 application, the end cap encloses only the outer edges of the axial ends of the pleats, and has an inner diameter larger than the diameter of the hollow interior defined by the inner pleat tips. The enlarged inner diameter of the end cap forms a radial seal with an enlarged outlet tube having a diameter greater than the diameter of the hollow interior defined by the inner pleat tips. A radial seal is formed between the enlarged diameter outlet tube and the enlarged inner diameter end cap at a location along the axial ends of the pleats between the inner pleat tips and the outer pleat tips. An outer liner circumscribes the filter element along the outer pleat tips and extends beyond the axial end thereof into the end cap and provides support for the noted radial seal, i.e. the end cap material is radially compressed between the outlet tube and the outer liner. The outlet flow passage from the filter element is now the inside diameter of the end cap rather than the diameter of the hollow interior defined by the inner pleat tips. Fluid passing through the filter media can now also travel axially between the pleats as well as axially through the hollow interior defined by the inner pleat tips. As a result of such construction, fluid flow restriction is reduced, and the radial depth of the pleat is no longer limited to a specific outlet tube diameter. Instead, the radial depth of the pleat can theoretically extend all the way to the axial center line of the filter, allowing maximization of filter media area within a given package or housing size. The invention of the ""714 application may also be used for opposite direction flow filters, in which case enlargement of the inlet flow passage is enabled, to reduce inlet flow restriction.
The invention of commonly owned copending U.S. application Ser. No. 09/527,792, filed Mar. 17, 2000, now U.S. Pat. 6,261,334, further increases flow capacity by enabling further enlargement of the outlet flow passage, to further lower the noted restriction to flow. The further increased outlet size of the filter element and the further lowered restriction is accomplished while still maintaining or even increasing the amount of filter media and while also staying within the same package or housing size. In the invention of the ""792 application, the largest diameter outlet from the filter element is not limited to the size of the diameter of the hollow interior defined by the inner pleat tips, nor limited to the inner diameter of the end cap even if the latter is enlarged in accordance with the invention of the ""714 application. The invention of the ""792 application enables the filter outlet to have a diameter substantially as large as the outer diameter of the filter element at the outer pleat tips. The invention of the ""792 application may be used for opposite direction flow filters, in which case maximized enlargement of the inlet flow passage is enabled, to minimize inlet flow restriction.
The invention of commonly owned copending U.S. application Ser. No. 09/616,188, filed Jul. 14, 2000, now U.S. Pat. 6,391,076, provides a full flow fluid filter wherein the fluid flows substantially directly axially through the filter element, lowering restriction to flow by minimizing bends or changes of direction in the flow pattern.
The above described filter constructions increase flow capacity and minimize restriction of primary or main filter elements. These open flow constructions have not lent themselves to the incorporation of a classical safety filter without decrease of filtration performance.
The role of a safety filter is to protect the engine during replacement of the main or primary filter element, or in case of failure or leakage of the main filter element. Separate sealing of the safety and main filter elements is required to allow for secure replacement of the main filter element. When failure occurs, the safety element is designed to plug quickly and shut down the engine. Safety filter elements typically have efficiencies less than that of the main filter element. The dust holding capacity of the safety filter element is low, usually less than 5% of the main filter element capacity. Adding a safety filter element to an air cleaner system generally increases the overall air cleaner restriction by 10-30%.
Adding a conventionally constructed safety filter element to the above described open flow filter constructions eliminates the advantages of the latter and/or leaves a bypass path which defeats the safety system.
The present invention provides a high capacity filter with an open flow main filter element and a safety filter element, and overcomes the above noted problems in a simple and effective manner.
The invention also provides a high capacity filter with a direct full flow main filter element and a safety filter element overcoming the above noted problems.
The invention further provides a filter construction with reduced overall restriction and increased filtering surface area.